Current semiconductor industry trends indicate that availability of lithography below 0.18 .mu.m is required for the development of high performance logic processors and 1-Gbit DRAM. In theory, there are two possible ways to get resist patterns with finer resolution, i.e. to shorten the wavelength of exposure light sources and to enlarge the numerical aperature (NA) of exposure systems.
KrF excimer laser (248 nm) steppers are widely used for the 0.25 .mu.m UV lithography manufacturing process of semiconductor devices. Due to the improvement of optical elements such as high NA optical elements, phase shift mask, etc., the 248 nm KrF scanners now are capable of offering pilot run of 0.18 .mu.m process and pioneer development of below 0.15 .mu.m process. However, since there is a limit for wavelength shortening, the processing or manufacturing of finer masks becomes more and more difficult. To meet the urge demand of minimizing the size of IC devices, development of 193 nm (ArF excimer laser) lithography and resists are recognized as an alternative resolution recently.
Unfortunately, due to the strong absorption of aromatic rings that provides dry-etch resistance, the conventional chemical amplified resists based on phenol resin (248 nm) are totally opaque at 193 nm. To solve the problems, new polymers that exhibit low optical density at 193 nm are in great need now.
Generally speaking, the polymers which are adequate candidates for the photoresists for 193 nm lithography are required to meet six basic requirements:
(1) high transparency for 193 nm light source; PA1 (2) good thermoplastic, ex. High glass transition temperature (Tg); PA1 (3) high etch resistance; PA1 (4) good adhesion and development for its composition; PA1 (5) contained acid labile functional groups; PA1 (6) be applied to general processes.
Recently, a tetrapolymer iBMA-MMA-tBMA-MMA (poly isobornyl methacrylate-methyl methacrylate-t-butyl methacrylate-methacrylic acid) is reported to be a possible resin system for ArF resist: ##STR2##
However, the tetrapolymer is also accompanied with undesirable adhesion and etch resistance. Therefore, a new resin for the compositions of resists is eager to be developed.